I have identical songs on different albums, e.g. on an artist album and on a 'best of'. I want to be able to play the tracks on either album - i.e. listen to the artist album or the 'best of' and hear the track - i.e. not remove it from either. But keep only 1 audio version of the song.

This is something that I would like to do also, as far as I know this is as close as one can get:

Make a playlist consisting of the "Best Of" (or movie soundtrack, or other compilation) tracks, then let Song Sergeant remove duplicates after manually choosing to keep the information associated with the original artist album in each case. The playlist will end up being comprised of tracks with "original artist" album information, and you can access the songs "by album" in the normal iTunes way.

Another approach to the same goal: After I rip a compilation or soundtrack CD, I make a playlist out of it and then use MPFreaker to overwrite with the oldest (original) album information for each track. In this way, I end up with the same kind of result.

I don't believe there is likely to be a better solution anytime soon, as iTunes (and other music organization software) stores metadata such as "album name" inside the track itself, and one simply cannot specify more than one album name.